[postgis-devel] Triangulation engine and constrainted polygontriangulation

Alexander Weidauer Weidauer at ifaoe.de
Sun Feb 2 10:30:07 PST 2014


Ok, hi maplabs, thanks that means, thats means all in.. a request for clearence

1. postgis_21_branch/liblwgeom/liblwgeom.h
2. Interfaces at SQL-MM and SimpleFeatures definitions
3. to investigate at JTS or Geos

How does interface building works in postgis?


Alexander  Weidauer

-------------------------------------------------------------------------------------------------
Dipl. Phys. A. Weidauer,  Fachbereich GIS/ EDV
Tel.: +49 (0) 38204 / 618-13
mail: weidauer at ifaoe.de
web: www.ifaoe.de<http://www.ifaoe.de/>
-------------------------------------------------------------------------------------------------

_
________________________________________
Von: maplabs at light42.com [maplabs at light42.com]
Gesendet: Sonntag, 2. Februar 2014 18:11
An: postgis-devel at lists.osgeo.org; Alexander Weidauer
Betreff: Re: [postgis-devel] Triangulation engine and constrainted      polygontriangulation

Hi Alexander -

  to respond, I am looking here:

  http://svn.osgeo.org/postgis/branches/2.1
  http://svn.osgeo.org/geos/branches/3.4/

  http://sourceforge.net/projects/jts-topo-suite/files/


--
  You may know, that PostGIS uses the GEOS library for a lot of the
computations. GEOS is a C++ port of selected JTS code.
(there is a second geometry engine in progress, but we wont think about
that now)

  You can see ST_DelaunayTriangles function definition here

    postgis_21_branch/extensions/postgis/sql/postgis.sql  Line 3202

resulting in a working function signature like this:

natural_earth2=# \df st_del*
List of functions
-[ RECORD 1 ]-------+------------------------------------
Schema              | public
Name                | st_delaunaytriangles
Result data type    | geometry
Argument data types | g1 geometry, tolerance double precision DEFAULT 0.0,
                        flags integer DEFAULT 0
Type                | normal

General triangle building and handing in PostGIS:

    postgis_21_branch/liblwgeom/lwtriangle.c

Type enumeration:

    postgis_21_branch/liblwgeom/liblwgeom.h
...
#define TRIANGLETYPE            14

=========
What does this mean?
   there are several directions to look for answers..

The Standards:
  There are formal SQL-MM and SimpleFeatures definitions, which serve as the
relevant guiding standards, towards which PostGIS is written.

The Geomtry Code Mothership - Java Topology Suite (JTS):
  Another are the exposed JTS routines, as above, which are callable.

Working Tests:
  Yet another direction for answers is the tests, which are included in the
PostGIS source tree. When new features are added to the project, good practice
is to add tests at the same time. For curious (and practical) people, the
tests are a good place to look for small working examples..

  postgis_21_branch/regress/delaunaytriangles.sql

  hmm, not so much there.. terse.. a big TODO at the top..

===============
So, in conclusion, I will infer the following:

  * Triangles in PostGIS are a defined type
  * some really really simple ops are defined in lwgeom
  * real computation on triangle comes from JTS
  * there has not been a lot of embellishment on PostGIS TRIANGLE to date

-------
Brian M Hamlin
OSGeo California Chapter
blog.light42.com

On Sun, 2 Feb 2014 13:44:26 +0100, Alexander Weidauer
<Weidauer at ifaoe.de> wrote:
Dear List, at the moment I use offline triangulation based on the
triangle tool of J. Schewchuck
(http://www.cs.cmu.edu/~quake/triangle.html) to manage, raster
interplation, fractal indexing, polygon aggragation... . I have seen,
that PostGIS 2.1 offers triangulation features
(ST_DelaunayTriangulation) now.
>
> I have some questions:
>
> 1. Which triangulation engine is used?
> 2. Where can I find it in in the repo how Are the maintainers?
> 3. Triangle has some smart an important features like mesh refinement
> (sizes and angles of the mesh), and !important constrained polygon
> triangulation. Are this features accessible in PostGIS 2.1?
>
> Thanks in advance Alexander  Weidauer
>
> -------------------------------------------------------------------------------------------------
> Dipl. Phys. A. Weidauer,  Fachbereich GIS/ EDV
> Tel.: +49 (0) 38204 / 618-13
> mail: weidauer at ifaoe.de
> web: www.ifaoe.de<http://www.ifaoe.de/>
> -------------------------------------------------------------------------------------------------
>
> _
>
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IfAÖ
Institut für Angewandte Ökosystemforschung GmbH
Mitglied der GICON® - Gruppe
Alte Dorfstrasse 11
18184 Neu Broderstorf
GERMANY

Telefon: +49 38204 618-0
Telefax: +49 38204 618-10
Geschäftsführung: Prof. Dr.-Ing. habil. Jochen Großmann (geschäftsführender Gesellschafter)
eingetragen beim Amtsgericht Rostock unter HRB 5324

Diese E-Mail enthält vertrauliche und / oder rechtlich geschützte Informationen. Wenn Sie nicht der richtige Adressat sind oder diese E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den Absender und vernichten Sie diese Mail. Das unerlaubte Kopieren sowie die unbefugte Weitergabe dieser Mail ist nicht gestattet.

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